Boiler shows A29, burner output limited, oxygen level control fault (if equipped)

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Failed Herz lambda sensor in flue, wiring fault to sensor, contamination of sensor tip, incorrect combustion settings

Safety: Flue gas components can be hot and contain CO. Allow cooling and ensure good ventilation.

Inspect sensor: Locate the lambda sensor in the flue and check for soot or condensate contamination. Clean gently if accessible.
Check cable: Ensure the sensor cable is intact and properly connected to the control module.
Do not bypass: Do not operate the boiler with the lambda sensor disconnected.
Technician service: A Herz technician should verify combustion and replace the lambda sensor if readings are out of range.

Professional Required 5/5

Herz lambda / O2 sensor

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